Outbreak locations.

<p>Map of Lombardy with the locations of the outbreaks arisen in the two epidemic periods (purple symbols: period 1, red symbols: period 2) and with municipalities color coded according to pig farm density (measured in herds per km²). The labels are referring to the provinces; BG: Bergamo, BS: Brescia, CO: Como, CR: Cremona, LC: Lecco, LO: Lodi, MN: Mantua, MI: Milan, PV: Pavia, SO: Sondrio, VA: Varese. We note that the average farm density across a whole municipality is generally lower than the actual local farm density around farm locations in that municipality.